1. Field of the Invention
The present invention relates to a liquid ejection head and a liquid ejection apparatus, and more particularly, to abnormal ejection determination technology in a liquid ejection head which ejects liquid from nozzles.
2. Description of the Related Art
In an inkjet system which ejects ink from nozzles by applying pressure to ink accommodated inside pressure chambers, a method has been proposed for measuring the pressure inside the pressure chambers by means of pressure sensors and thereby ascertaining the ejection state of the ink. The pressure wave generated in a pressure chamber is high-speed and high-frequency, and the measurement signal obtained from the pressure sensor is a signal having a very weak voltage. Therefore, the difference between normal operation and abnormal operation is small, and hence it is difficult to distinguish between normal operation and abnormal operation. Various methods have been proposed in order to accurately judge normal operation and abnormal operation from a measurement signal having a very weak voltage of this kind.
Japanese Patent Application Publication No. 7-132592 discloses that a measurement drive pulse is applied to a piezoelectric element prior to a printing operation, and the pressure variation inside the pressure chamber is measured by means of the piezoelectric element and the measurement circuit, in addition to which a drive waveform is calculated on the basis of the characteristics of this pressure variation, and during printing, a drive voltage waveform is applied to the piezoelectric element on the basis of the calculated drive waveform.
Japanese Patent Application Publication No. 55-118878 discloses that a measurement device is provided in order to determine the state of displacement of a vibrating element which deforms an ink chamber in response to an electrical signal, and the state of displacement of the vibrating element with respect to the electrical signal is evaluated.
Japanese Patent Application Publication No. 6-155733 discloses that drive pulse signals are applied to a piezoelectric element by a drive element and the piezoelectric element thereby deforms a plurality of times in a short period of time so that the ink inside the ink chamber is gradually ejected and one ink droplet is formed by this ink. During this, a determination device determines the variation in the ink inside the ink chamber at each occurrence of a prescribed pulse of the drive pulse signal, and a control device controls the drive element in such a manner that a pulse following the prescribed pulse is generated on the basis of the determination results of the determination device.
In general, a method for determining the pressure in a pressure chamber includes a method of determining pressure abnormalities by measuring the absolute amplitude of the pressure wave, or a method of determining pressure abnormalities by measuring the frequency characteristics of the pressure wave. In the method that measures the absolute amplitude of the pressure wave, if there is not a very large difference between the absolute amplitude of the pressure wave during normal operation and the absolute amplitude of the pressure wave during abnormal operation, then it becomes difficult to accurately judge between normal operation and abnormal operation. In the method that measures the frequency characteristics of the pressure wave, the system for measuring the frequency of the pressure wave is complicated. More specifically, a composition is possible in which the frequency is measured by using a frequency filter, such as a low-pass filter, a high-pass filter, or a band-pass filter, and in a composition of this kind, there is a problem in that a filter device must be provided in the signal processing unit which processes the signal obtained from the sensors, and therefore the system becomes complicated.
In Japanese Patent Application Publication No. 7-132592, the measurement drive signal is required in order to determine the pressure variation within the pressure chamber, and therefore a device for generating this measurement drive signal, and a storage device for storing the measurement drive signal, are necessary. Hence, there is a problem in that the control system becomes large in scale.
In Japanese Patent Application Publication No. 55-118878, a high-pass filter for acquiring a high-frequency component from the measurement signal is required, and there is a problem in that the circuitry of the signal processing system becomes large in scale.
In Japanese Patent Application Publication No. 6-155733, a timing circuit is required in order to determine the residual vibration of the pressure chamber at each occurrence of a prescribed number of pulses, and furthermore, the calculation unit that generates a subsequent pulse on the basis of the residual vibration must be capable of high-speed processing.